DENVER — Mitt Romney is set to kick off the most important stretch of his presidential campaign, a time when he said he will use his three debates with President Obama to set the record straight on his vision for the country and to stump more vigorously in swing states.

The Republican nominee spent the weekend huddled with advisers and with Sen. Rob Portman (R-Ohio), who has been playing Obama in mock debate sessions.

Romney said the debates, the first of which is Oct. 3, will give him a chance to push back against what he said were distortions by the Obama campaign on the auto bailout, his record on abortion and tax rates for the middle class.

“I think what we can do is have a chance for people to see our respective positions and our pathways forward. I think the president will not be able to continue to mischaracterize my pathway and so I’ll be able to describe mine, he will describe his and people will make a choice,” he said on his campaign plane, with Portman by his side. “That’s the great thing about democracy. I’m not going to try and fool people into thinking he believes things he doesn’t. He’s trying to fool people into thinking that I think things I don’t. And that ends, I think, during the debates.”

Romney has faced criticism from fellow Republicans who have said his campaign needs an overhaul and a clearer message.

He is set to tour Ohio this week with his running mate, Rep. Paul Ryan (Wis.). Polls in key swing states show Romney trailing Obama — in Colorado, where Romney held a rally Sunday evening, he trails Obama among likely voters 50 percent to 45 percent.

“I know in the coming six weeks they’re very unlikely to remain where they are today,” he said. “I’ll either go up or I’ll go down. It’s unlikely that we’ll just stay the same.”